Rocky Mountain Institute’s four scenarios for the future U.S. electricity system ( detailed here ) all have markedly different projected CO2 emissions over the next 40 years.
The Intergovernmental Panel on Climate Change (IPCC) has proposed a target of 80% emissions reductions from 2000 levels by 2050 to stabilize atmospheric CO2 concentration below 450 parts per million (ppm) and avoid the most serious effects of climate change. With the fossil-fuel heavy resource mix in the Maintain (“business-as-usual”) case, U.S. CO2 emissions from electricity generation would continue to rise, reaching a 2050 emissions level 500% higher than the IPCC target applied to the U.S. electricity sector.
Despite the heavy adoption of nuclear and IGCC/CCS generators, the Migrate case still falls short of the IPCC goal, mainly because the system still requires a flexible (peaking) generation source. The most economical choice is natural gas, whose CO2 emissions help keep the Migrate case from meeting the IPCC goal. A costlier but cleaner peaking resource, such as thermal or battery storage, would allow the Migrate case to meet the IPCC target.
RMI’s Renew and Transform scenarios for the future U.S. electricity system reach very similar CO2 emissions levels of around 130 million tons annually in 2050, well below the IPCC emissions target. These two cases are both built around an electricity grid dominated by renewables—though the scales are different. Renew relies mostly on utility-scale renewable projects, while Transform uses an intelligent microgrid network powered largely by distributed renewables.
Anon. 2007. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007. Cambridge: Cambridge University Press.
U.S. Energy Information Administration. 2009. Emissions of Greenhouse Gases in the United States 2008. Washington, D.C.: U.S. Department of Energy, December. link